JP2010500595A - Method and detector for measuring and / or judging afterglow of ceramic materials - Google Patents

Abstract

The present invention relates to a method for measuring and / or determining the afterglow of ceramic materials, in particular Gd ₂ O ₂ S materials and / or precursor materials, by measuring Eu, Tb and / or Yb content. .

Description

The present invention relates to a method for measuring the afterglow of ceramic materials, in particular Gd ₂ O ₂ S materials.

  Fluorescent members for detecting high energy radiation include phosphors that can absorb radiation and convert it to visible light. The luminescent emission produced thereby is obtained and evaluated electronically with the aid of a light sensitive system such as a photodiode or a photomultiplier tube. Such a fluorescent member can be manufactured from a single crystal material such as a doped alkali halide. Non-single crystalline materials can be used as powdered phosphors or in the form of ceramic members made therefrom.

A typical fluorescent ceramic material used to detect 10-200 keV x-ray radiation is doped Gd ₂ O ₂ S, for example doped with Ce ³⁺ or Pr ³⁺ . However, if Gd ₂ O ₂ S exhibits a luminescent property known as “afterglow”, ie after the desired immediate fluorescence (determined by the specific emission time of the particular activator ion used ) Use of Gd ₂ O ₂ S is somewhat reduced if a “second fluorescence” can be seen that is somewhat darker but lasts longer and can occur at a wavelength different from the immediate fluorescence . In other words, afterglow can be defined as a non-instantaneous response of a stationary scintillator signal after the scintillator X-ray photon exposure is turned off. This residual signal is sometimes referred to as lag, or often referred to as afterglow. The afterglow is given as a relative value to the stationary signal of the scintillator material under examination and is usually evaluated as a function of time after the end of the X-ray pulse. In CT, the associated time domain of the afterglow signal is between 0.1 ms and 2 s, while the value is less than 300 ppm at 5 ms and 0.5 s to ensure an artifact-free CT image. Must be well below 20 ppm. Afterglow is one of the key performance criteria for scintillators in CT applications.

The first object of the present invention is to provide a method by which the afterglow of Gd ₂ O ₂ S material can be effectively measured.

This object is solved by a ceramic material according to claim 1 of the present invention. Accordingly, a method for measuring and / or determining the afterglow of a Gd ₂ O ₂ S: M fluorescent ceramic material, wherein M is a group of Pr, Dy, Sm, Ce, Nd and / or Ho and / or said A method is provided that represents at least one component selected from a precursor material of a ceramic material. Thereby, afterglow is measured and / or determined by measuring Eu, Tb and / or Yb concentrations in the fluorescent ceramic material and / or precursor material.

Surprisingly, the inventor can measure and / or determine the afterglow of a Gd ₂ O ₂ S material by measuring the Eu, Tb and / or Yb concentration in the material. I found something. Furthermore, the present inventor, for a wide range of applications within the scope of the present invention, the _{Gd 2 O} 2 S Eu precursor substance of the material, by measuring the Tb and / or Yb _{concentration,} Gd _{2 O} 2 S It has been found that the afterglow of the material can be measured and / or determined.

The term “precursor material” in the sense of the present invention means and / or includes the material from which the Gd ₂ O ₂ S material is produced. A list of non-limiting examples of precursor materials is GdCl ₃ , GdBr ₃ , GdI ₃ , Gd (NO ₃ ) ₃ , Gd ₂ (SO ₄ ) ₃ GdF ₃ , Gd ₂ S ₃ , Gd ₂ O ₃ , Gd ₂ (CO ₃ ) ₃ , Gd ₂ (C ₂ O ₄ ) ₃ , and individual salts of metal M selected from the group of Pr, Dy, Sm, Ce, Nd and / or Ho.

Without being limited to any particular theory, the inventor believes that many roles of Eu in causing afterglow of Gd ₂ O ₂ S materials are due to at least the following mechanisms:

During processing of the fluorescent ceramic material, the portion of the metal M in Gd ₂ O ₂ S that is normally present in the form of trivalent ions is oxidized as represented by Formula I:
M ³⁺ −> M ⁴⁺ + e ⁻ (I)

When M is praseodymium (which is a preferred embodiment of the present invention), this equation is shown as Formula Ia:
^{Pr 3+ -> Pr 4+ + e} - (Ia)

Some of the electrons released by Formula I (or Ia) react with Europium as shown in Formula II:
Eu ³⁺ + e ⁻ −> Eu ²⁺ (II)

These Eu ²⁺ ions are further oxidized by hole trapping and return to Eu ³⁺ ions. However, these Eu ³⁺ ions are in an excited state and then emit light in the wavelength range of about 400-750 nm (several emission lines) with its most prominent emission in the range 580-640 nm, A substantial overlap with the Pr ³⁺ emission spectrum (formula III) is shown.
h ⁺ + Eu 2 ⁺ -> Eu ³⁺ + hν (400-750 nm) (III)
This results in an undesirable afterglow of the ceramic material.

  In contrast, the afterglow contribution by Tb is not caused by the mechanism described for Eu. Here, the intrinsic decay of the excited Tb ions plays a dominant role. This indicates that the associated time domain of the afterglow signal is 10 ms or less, thus only affecting the so-called short-term afterglow domain (<20 ms).

  However, in the case of Yb, the inventor believes that the mechanism is similar to Eu and has a significant impact that leads to undesirable afterglow in the full time domain (0.1 ms to 2 s) associated with CT.

In fact, Yb reacts similarly to the Eu reaction found in Formula III, as shown in Formula IV:
h ⁺ + Yb ²⁺ −> Yb ³⁺ + hν (about 980 nm) (IV)

  According to a preferred embodiment of the present invention, the method according to the present invention includes time-delayed spectroscopy.

The term “time-delayed spectroscopy” in the sense of the present invention means in particular the end of excitation of the ceramic material and / or precursor material at time T ₀ and the delayed start of measurement after time T _1. And / or include.

The preferred embodiment of the present invention, the time _{T 0} is the ^{(Pr 3+} and / or ^Eu 3+, ^{Yb 3+,} other) the intensity of the laser pulses for exciting the emission is lower time than 1% of the highest intensity Now, this means that T ₀ is defined as the starting point for any delayed light emission process.

  In this embodiment, it is particularly preferred that the laser pulse waveform and in particular its falling edge has a time difference defined by a time stamp corresponding to, for example, a 99% intensity level and a 1% intensity level, and any associated inherent characteristic. Or it must be chosen to be smaller than the delayed luminescence process. This time difference is preferably less than 1% of the fastest emission decay time to ensure spectroscopic fingerprint measurements delayed by an appropriate time.

T ₁ is, for example, a time spectroscopy measurements are time delays using the CCD camera is initiated, T ₂ is the measurement is stopped time.

  According to a preferred embodiment of the present invention, the measurement includes measuring the emission of a material in the wavelength range of 370 nm to 1100 nm, preferably 600 nm to 1050 nm.

According to a preferred embodiment of the present invention, T ₁ -T ₀ is not less than 1 μs and not more than 1000 μs, preferably not less than 20 μs and not more than 500 μs. This increases the accuracy of afterglow measurement or judgment for a wide range of applications within the scope of the present invention.

According to a preferred embodiment, in a wide range of applications, T ₁ -T ₀ is advantageously at least 20 μs to prevent detection of direct (non-delayed) Pr ³⁺ emission, otherwise It has been found that it dominates any luminescence process.

  According to a preferred embodiment of the present invention, the time-delayed spectroscopy can excite a ceramic material or precursor material having at least one wavelength in the wavelength region of 100 nm to 300 nm, preferably 240 nm to 270 nm. Including.

According to a preferred embodiment of the invention, the time delayed spectroscopy is stopped after time T ₂ , where T ₂ −T ₁ is 500 ms or more, preferably 1 s or more.

According to a preferred embodiment of the invention, the time delayed spectroscopy is stopped after time T ₂ , where T ₂ −T ₁ is 2 s or less, preferably 1.5 s or less. More preferably, it is 1 s or less.

Within the broad application of the present invention, selecting T ₂ as described above is actually advantageous because sufficient information can be gathered, but if T ₂ is too long, the signal / noise ratio Has been found to be disadvantageous.

It should further be noted that according to another embodiment of the present invention, the emission spectrum during laser excitation can be measured to also determine the Pr ³⁺ emission spectrum. However, this spectrum also includes small contributions such as Eu ³⁺ , Yb ³⁺ etc. in many applications. After measuring the time-delayed emission spectrum and the Pr emission spectrum, the intensity ratio of these emission bands of these spectra can also be analyzed to obtain quantitative information. As mentioned above, T ₁ -T ₀ can also be used to obtain other insights (intensity ratio as a function of delay time).

  According to a preferred embodiment of the present invention, the method includes time-resolved spectroscopy.

  The term “time-resolved spectroscopy” particularly means and / or includes a continuous measurement over a specific time, the specific time being preferably not less than 50 μs and not more than 1 s, more preferably not less than 100 μs and not more than 500 ms. It is as follows.

  According to a preferred embodiment of the present invention, the time-resolved spectroscopy is a ceramic material or precursor having at least one wavelength in the wavelength region from 600 nm to 650 nm, in particular to determine the Eu concentration and the corresponding afterglow contribution. Includes measurement of luminescence of body material.

  According to a preferred embodiment of the present invention, the time-resolved spectroscopy is a ceramic material or precursor having at least one wavelength in the wavelength range from 930 nm to 1100 nm, in particular to determine the Yb concentration and the corresponding afterglow contribution. Includes measurement of luminescence of body material.

  According to a preferred embodiment of the present invention, time-resolved spectroscopy is performed at least 1 in the wavelength region from 370 nm to 570 nm (more preferably from 530 nm to 560 nm) in order to determine the Tb concentration and the corresponding afterglow contribution. Including the measurement of the emission of a ceramic material or precursor material having two wavelengths.

According to a wide range of applications within the scope of the present invention, the above-mentioned region for the determination of Eu, Tb and / or Yb eliminates or ignores any additional contribution from other Pr ³⁺ emission lines. It should be noted that it is chosen so that it can. In this way, the intensity of the afterglow signal (eg caused by time-delayed Eu ³⁺ , Tb ³⁺ and / or Yb ³⁺ luminescence) is obtained as a normalized group Pr ³⁺ to obtain a time-resolved afterglow curve. The luminescence intensity can be measured at any time.

  According to another and preferred embodiment of the invention, the information used is also the intensity ratio of the examined spectral region as a function of time.

  According to a preferred embodiment of the present invention, the time-resolved spectroscopy comprises excitation of a ceramic material or precursor material having at least one wavelength in the wavelength region of 100 nm to 300 nm, preferably 240 nm to 270 nm.

  According to a preferred embodiment of the present invention, the method includes continuous excitation spectroscopy.

  The term “continuous excitation spectroscopy” means and / or includes, in particular, the measurement of the emission of ceramic materials or precursor substances in specific different wavelength ranges, which measurement includes the Eu, Tb and / or Yb concentration. Compared to each other to get. The term “continuous excitation spectroscopy” specifically means and / or includes that a continuous light source is used, and again the photon energy is selected such that the excitation is through the band gap. The emission spectrum is measured, for example, via a CCD camera.

  According to a preferred embodiment of the present invention, the continuous excitation spectroscopy is a ceramic having at least one wavelength in the wavelength region from 600 nm to 650 nm, in particular to determine the Eu concentration and to determine the corresponding afterglow contribution. Includes measurement of luminescence of material or precursor material.

  According to a preferred embodiment of the present invention, the continuous excitation spectroscopy is a ceramic having at least one wavelength in the wavelength range from 930 nm to 1050 nm, in particular to determine the Yb concentration and to determine the corresponding afterglow contribution. Includes measurement of luminescence of material or precursor material.

  According to a preferred embodiment of the present invention, continuous excitation spectroscopy is performed in the wavelength region of 370 nm to 570 nm, more preferably 530 nm to 560 nm, in order to determine the Tb concentration and to determine the corresponding afterglow contribution. The following wavelength regions include measurement of the emission of a ceramic material or precursor material having at least one wavelength.

The present invention further provides a detector for measuring the afterglow of a Gd ₂ O ₂ S: M fluorescent ceramic material, wherein M is Pr, Dy, Sm, using one or more of the methods described above. It relates to a detector which represents at least one component selected from the group of Ce, Nd and / or Ho and / or a precursor material of said ceramic material.

  According to one embodiment of the present invention, the detector preferably comprises a laser such as a CCD-based detector and / or a YAG-based laser with a spectrally variable detection range that is time-gated.

The invention further relates to the use of the detector and / or the use of any of the methods described above in one or more of the following systems:
-A system adapted for medical imaging.
A system for judging the quality of Gd ₂ O ₂ S: M fluorescent ceramic materials. M represents at least one component selected from the group of Pr, Dy, Sm, Ce, Nd and / or Ho and / or precursor materials.
A system for producing a Gd ₂ O ₂ S: M fluorescent ceramic material. M represents at least one component selected from the group of Pr, Dy, Sm, Ce, Nd and / or Ho.

  The components described above, the claimed components, and the components used in accordance with the present invention in the described embodiments are such that selection criteria known in the relevant field can be applied without limitation. , Without any special exceptions regarding their size, shape, material selection and technical concepts.

  Additional details, characteristics and advantages of the object of the invention are disclosed in the dependent claims, the figures and the following description of the individual drawings and examples which show by way of example preferred embodiments of the detector according to the invention.

According to the first embodiment of the present invention, the intensity vs. the emission (bottom) of a probe delayed using an a-timed I-time delayed spectroscopy (top) and b) Two very schematic diagrams of time. The figure which shows the emission spectrum of the 1st GOS powder measured by the time-delayed spectroscopy. FIG. 5 shows emission spectra of different GOS powders measured by time delayed spectroscopy. The figure which shows the afterglow spectrum of two GOS ceramics produced | generated from the GOS powder of FIG.2 and FIG.3. FIG. 3 is a very schematic diagram of a detector according to another embodiment of the invention.

  FIG. 1 shows a) I time-delayed spectroscopy using a laser pulse (top), and b) emission of a probe excited using a laser, according to a first embodiment of the invention (bottom). Shows two very schematic diagrams of intensity versus time. It should be emphasized that both curves are very schematic and are only used to illustrate a time delayed spectroscopy process.

In FIG. 1, time T ₀ is shown when the intensity of the laser pulse (its intensity is shown in the upper diagram) is less than 1% of its highest intensity, and T ₀ is any delayed emission. It is defined as the starting point for the process. “99%” — intensity—time is indicated as “T- ₁ ”.

In this embodiment, the laser pulse waveform and in particular edge falling its falling, for example the time difference is defined by the time stamp corresponding to the 99% intensity level ( "T _-1") and 1% of the intensity level "T _0" is The probe was chosen to be smaller than any associated intrinsic or delayed luminescence process.

The time indicators “T ₁ ” and “T _2” indicate when the measurement is started and stopped. However, Figure 1 is a highly schematic, T ₂ should be more attention to long for most applications.

FIG. 2 shows the emission spectrum of the first GOS powder measured by time-delayed spectroscopy. The time delay (= T ₁ −T ₀ ) is 10 ms after the laser pulse in the wavelength region of 266 nm. T ₀ was set as described in FIG.

  From the spectrum, it can be obtained that the Eu content is very low (ie <1 ppm Eu), while there is a small content of Tb (peak near 540 nm). As shown in FIG. 4, this Tb content results in a time domain afterglow of 10 ms or less (short-term afterglow).

FIG. 3 shows the emission spectra of different GOS powders measured by time-delayed spectroscopy. Again, the time delay (= T ₁ −T ₀ ) is 10 ms after the laser pulse in the 266 nm wavelength region. T ₀ was set as described in FIG.

  From the spectrum, it can be obtained that the Eu content is approximately 10 ppm.

  It should be noted that the intensities in FIGS. 2 and 3 cannot be directly compared. In FIG. 3, the Eu emission peaks near 620-630 nm and 700 nm are much higher than the small Tb contribution near 540 nm, which is just under 10 ms (short-term afterglow), similar to the GOS powder of FIG. Bring time domain afterglow.

  FIG. 4 shows the afterglow spectra of two GOS ceramics produced from the GOS powders of FIGS. Two GOS ceramics were produced from GOS powder according to EP-A-0 511 0054.3. The contents of this publication are incorporated herein by reference.

  In FIG. 4, the afterglow spectrum of the GOS ceramic made from the GOS powder of FIG. 2 is indicated by a dot symbol (“•”), and the afterglow spectrum of the GOS ceramic made from the GOS powder of FIG. , Indicated by a plus sign (“+”).

  It can be seen that GOS ceramics made from powders with lower Eu content have a significantly lower afterglow. In fact, only this ceramic is considered acceptable.

  However, due to the fact that both GOS ceramics were made from powder mixed with a small amount of Tb, there is a slight increase in afterglow curve visible in the time zone around 1 ms (different slope of afterglow curve). However, in both ceramics, the Tb content is low enough not to cause unacceptable afterglow, but according to the invention, this short-term afterglow can be measured as well and / or Can be judged.

  In FIG. 4, it should be noted that the effect of the measuring device (which prevents showing afterglow) dominates the shape of the afterglow curve below 600 μs.

In the present invention, an acceptable GOS ceramic is defined as having an afterglow lower than 20 * 10 ⁻⁶ after 0.5 s. This point is indicated by the two thick lines in FIG. It can clearly be seen that only GOS ceramics made from the powder of FIG. 2 are acceptable and other GOS ceramics are not acceptable.

Thus, for a wide range of applications within the scope of the present invention, simply _Gd 2 _O 2 S: from measurements of Eu in M fluorescent ceramic material, Tb and / or Yb content, the _Gd 2 _O 2 S: M fluorescent ceramic material It is possible to identify whether it has an acceptable afterglow, where M is from a group of Pr, Dy, Sm, Ce, Nd and / or Ho and / or a precursor material of said ceramic material Represents at least one selected component.

For a wide range of applications within the scope of the present invention, the afterglow of the final Gd ₂ O ₂ S: M fluorescent ceramic material can be estimated from the Eu, Tb and / or Yb content of the precursor material. As such, the production effectiveness and / or yield of these Gd ₂ O ₂ S: M fluorescent ceramic materials can be greatly increased.

  FIG. 5 shows a very schematic view of the detector 1 according to another embodiment of the invention. The detector has an Nd: YAG-laser 10 that emits light having a wavelength of λ = 1064 nm towards the material 20 to be characterized. In the optical path, a frequency quadruple unit 15 for changing the wavelength to λ = 266 nm is provided. The spectrum of the material 20 is characterized by a CCD detector 40 that is synchronized by the trigger unit 30. CCD detectors have a spectrally variable detection range that is time-gated. Finally, the data is collected and analyzed by computer 50.

  The specific combinations of components and features of the detailed examples described above are exemplary only; the exchange of these teachings with other teachings in this specification and patent specifications / applications incorporated by reference and Replacement is also explicitly contemplated. Those skilled in the art will recognize that variations, modifications, and other implementations of what is described herein do not depart from the spirit and scope of the invention as described in the claims. Would come up with. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The scope of the present invention is defined in the appended claims and equivalents thereof. Furthermore, reference signs used in the detailed description and claims do not limit the scope of the invention as recited in the claims.

Claims (10)

Gd ₂ O ₂ S: a measuring the afterglow of M fluorescent ceramic materials and / or methods for determining, M is, Pr, Dy, Sm, Ce , Group Nd and / or Ho and / or the ceramic material Wherein the afterglow is measured by measuring the Eu, Tb and / or Yb concentration of the fluorescent ceramic material and / or precursor material and / or The method to be judged.   The method of claim 1, wherein the method comprises time delayed spectroscopy. The time delayed spectroscopy includes the end of excitation of the ceramic material or precursor material at time T ₀ and the delayed start of the measurement after time T ₁ , where T ₁ -T ₀ is , 15 μs or more and 1000 μs or less,
Spectroscopy to be the time delay is stopped after a time _{T 2, where,} T 2 -T ₁ is 500 ms or more, preferably at least 1s, the method according to claim 1 or 2.   4. A method according to any one of the preceding claims, wherein the time-delayed spectroscopy comprises measuring the emission of the material in a wavelength range of 370 nm to 1100 nm, preferably 600 nm to 1050 nm.   The method according to claim 1, wherein the method comprises time-resolved spectroscopy. The time-resolved spectroscopy is
In particular, to determine the Eu concentration and the afterglow contribution, including emission of the ceramic material or precursor material having at least one wavelength in the wavelength region of 600 nm to 650 nm and / or in particular the Yb concentration and the afterglow In order to determine the contribution, including the emission of the ceramic material or precursor substance having at least one wavelength in the wavelength region of 930 nm to 1050 nm and / or in particular to determine the Tb concentration and afterglow contribution, Including emission of the ceramic material or precursor substance having at least one wavelength in a wavelength region of 370 nm or more and 570 nm or less,
6. A method according to any one of claims 1-5.   7. A method according to any one of claims 1 to 6, wherein the method comprises continuous excitation spectroscopy. The continuous excitation spectroscopy is
In particular, to determine the Eu concentration and the afterglow contribution, including emission of the ceramic material or precursor material having at least one wavelength in the wavelength region of 600 nm to 650 nm and / or in particular the Yb concentration and the afterglow In order to determine the contribution, including the emission of the ceramic material or precursor substance having at least one wavelength in the wavelength region of 930 nm to 1050 nm and / or in particular to determine the Tb concentration and afterglow contribution, Including emission of the ceramic material or precursor substance having at least one wavelength in a wavelength region of 370 nm or more and 570 nm or less,
The method according to any one of claims 1 to 7. A detector for measuring the afterglow of a Gd ₂ O ₂ S: M fluorescent ceramic material, wherein M is Pr, Tb, Dy, Sm, Ce and by the method of any one of claims 1-8. A detector representing at least one component selected from the group of Ho and / or the precursor material of the ceramic material. Use of a detector according to claim 9, and / or a system adapted for medical imaging;
A system for determining the quality of a Gd ₂ O ₂ S: M fluorescent ceramic material, wherein M is at least selected from the group of Pr, Dy, Sm, Ce, Nd and / or Ho and / or precursor materials One component, the system;
A system for producing a Gd ₂ O ₂ S: M fluorescent ceramic material, wherein M represents at least one component selected from the group of Pr, Dy, Sm, Ce, Nd and / or Ho; ,
Use of the method according to any one of claims 1 to 8 in one or more of the above.

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